Field of the Invention
The invention relates to a method for determining the mass of wet laundry in a washing machine drum being drivable by an rpm-controlled universal motor, with the aid of controller variables.
One such method is known from Published European Application No. 410 827. In that method, the mass of laundry is determined during the startup phase at constant acceleration. In that phase, the phase angle and the magnitude of the supply voltage are measured, and are used to calculate the mass inertia of the laundry by taking engine constants and the acceleration performance of the empty drum into account. Since the drum dimensions and the acceleration are known, a conclusion as to the mass can also be drawn from the calculated value for the mass inertia. Since the laundry in the drum still tumbles about forcefully during the startup process until it has distributed itself firmly in a ring of laundry on the inside of the drum wall, it is extraordinarily difficult to keep the acceleration constant from phase to phase. Deviations from the command value for the acceleration can therefore not be precluded. Occasionally, a uniform ring of laundry may not be attainable either, for instance because the laundry load includes relatively large pieces that are incapable of uniform fixation in the ring of laundry since their centers of gravity are sometimes much closer to the axis of the drum, and the requisite centrifugal force is not imparted to them. In such cases, the measurement of the supply voltage phase angle becomes imprecise, because even the slightest deviations from the even number of drum revolutions during the startup phase are expressed in major inaccuracies. Moreover, the measurements of the magnitude of the supply voltage and of the phase angle require special instruments, which are not otherwise needed for controlling the speed of the universal motor.